1. Field of the Invention
The present invention relates to organic grouting compositions for anchoring a reinforcing member in a hole, e.g., in a mine roof, and more particularly to those compositions comprised of a resin component containing an unsaturated polymerizable polyester resin and a monomeric polymerizable ethylenic cross-linking agent therefor, and a peroxide catalyst component, which is maintained separate from the resin component until the time of use and, when mixed therewith around a reinforcing member in a hole, catalyzes the rapid reaction of the polyester and ethylenic monomer to form a hardened grout.
2. Description of the Prior Art
Anchor bolts are employed in various fields of engineering, for example, as strengthening or reinforcing members in rock formations and in structural bodies. The bolts are inserted into drill holes in the formation or body, and often are fixed or anchored therein, at their inner end or over substantially their entire length, by means of a reactive grouting composition which hardens around the bolt. When used in a mine roof, bolts grouted in this manner help significantly to prevent mine roof failure. Because unsupported rock strata have a tendency to move vertically and laterally, and this motion is what commonly causes the roof to fail, it is important that bolts be installed as soon as possible in a newly exposed roof and that the required strength provided by the hardening of the grouting composition be developed rapidly, e.g., in a matter of a few minutes, or within an hour or so, depending on the type of mine. Rapid hardening also contributes to the efficiency of the bolt installation operation.
Reactive grouting compositions which have been used in rock bolt anchoring include inorganic cement mortars and hardenable synthetic resins, and these have been introduced into the drill holes through a feed pipe, or in cartridged form. Although the reactive ingredients of the composition can be delivered into the hole in combined and mixed form either before or after bolt insertion, usually they have been delivered separately into the hole, e.g., in compartmented cartridges, and combined therein and mixed, e.g., by inserting the bolt into the cartridges and rotating it.
A hardenable synthetic resin composition that has gained wide acceptance as a bolt-anchoring grouting composition is a composition containing an unsaturated polymerizable polyester resin and a monomeric polymerizable ethylenic cross-linking agent therefor. These materials, together with a polymerization inhibitor or stabilizer, and a promoter for a peroxide catalyst, constitute a resin formulation contained in a first grouting component (A). A cross-linking peroxide catalyst system is contained in a second grouting component (B), kept separated from component A until the hardening reaction is to take place. When components A and B are combined and mixed, the action of the catalyst causes the cross-linking reaction between the polyester and ethylenic monomer to take place, resulting in a thermoset, hard resin.
U.S. Pat. Nos. 3,324,662, 3,324,663, and 3,302,410, all granted to D. C. McLean, describe a two-component resin composition of this type which additionally contains 5 to 10 percent (based on final resin volume) of a water-receiver filler in one of the components, and water in the other component in at least an amount sufficient to react with at least a substantial portion of the water-reactive filler and also minimize shrinkage. The composition also contains a thickener such as pyrogenic silica, and only optionally an inert filler for the sole stated purpose of reducing the unit volume cost of the resin. In McLean's preferred composition, water is emulsified in the resin using an emulsifying agent, and the peroxide catalyst is mixed with cement.
The use of water in the above-mentioned compositions is associated with the presence of a water-reactive filler therein. Indeed, the amount of water indicated to be usually preferred is about that which will react with the water-reactive filler, and even only half of this amount is said to give good results. When used in this manner, i.e., combined with a water-reactive filler such as cement, water is disclosed to reduce shrinkage of the resin.
U.S. Pat. No. 3,731,791, issued to Fourcade et al., describes the use of a peroxide-catalyzed cross-linkable unsaturated polyester resin system in a single-compartment cartridge wherein the resin component and the catalyst component are separated solely by a layer of reaction product formed when the two components are brought into direct contact with each other. Although water is present in one of the resin components and one of the catalyst components described, the patentees nevertheless disclose the use of inorganic fillers such as calcite principally to reduce the shrinkage of their resinous mass which is said to always occur during polymerization.
The gel time of a given resin formulation is the time that elapses between the mixing of the reactive components and the hardening or stiffening of the resin. It will be shorter at higher temperatures and/or with higher promoter content, and vice versa. The cure time, on the other hand, is the time required for the composition to achieve full strength, or a high percentage of its final strength. A desirable goal is that the composition attain about 80% of its final strength in an hour or less. It is especially important that as strong as possible an interfacial bond between the resin and the wall of the hole, and the resin and the reinforcing member, be achieved during the curing period inasmuch as the advantageous keying effect achieved by a shifting of rock strata relative to one another usually is not available during this period because the roof has only recently been exposed.